Generally speaking, optimum sump temperature is 80-100C. Sump temperatures up to ~120C are ok, albeit with increased oil oxidation.

Oil warm up is slow-much slower than coolant. 15-20 minutes from cold start would be a ball park figure. Oil temperature sensors located in the oil return line give a false perception since the important figure during warm-up is the temperature of the oil entering the system.

The optimum sump oil temperature is dependant on how heavily the engine is loaded (optimum temperature inversely proportional to load).

Optimum oil temperature also depends on engine speed (optimum temperature increases with RPM)

There's not a great deal you can do to tightly control the temperatures but if you go easy for the first 10-15 minutes, you'll minimise wear.

Oil temperature has a strong dependancy on RPM, so you can use engine braking to help warm up the oil if you're concerned.

Bathtub Tom isn't wrong; most engines survive a complete disregard for oil temps :)

Some cars do get a fluid-to-fluid cooler/heater for the engine oil - both my Subaru Outback and Hyundai Santa Fe had/have them - I only discovered when removing undershields to do oil changes and discovered an unexpected device next to the oil filter with pipes which lead back to the cabin heater circuit.

As the engine coolant is running at 85-90 degrees C, consistently in all normal conditions this provides a very stable temperature for the engine oil (and autobox fluid in many cases) to equalise to.

An oil pressure gauge is the most inportant indicator as to whether an engine is warm enough to thrash. Sadly not many cars are fitted with them these days. Generally water temperature gauges are in their "normal" zones way, way before the oil is warm enough, the only way to tell the engine oil is warm enough is that the oil pressure drops off at idle.